Polyvinyl acetate emulsion containing an aromatic amide, and a base coated therewith



Patented May 6, 1952 POLYVINYL ACETATE EMULSION CONTAIN- ING AN AROMATICAMIDE, AND A BASE COATED THEREWITH Walter G. Kunze and Raymond BertramEvans,

Catonsville, Md., assignors to Le Page's Inc., Gloucester, Mass, acorporation of Massachusetts No Drawing. Application April 6, 1950,Serial No. 154,430

6 Claims.

This invention relates to emulsions of polymers which are suitable foruse as coatings and as adhesives. It is particularly concerned with suchan emulsion of polymers which is capable of providing a water-resistantbond or coating and which at the same time retains the stability,fluidity and the various other physical properties of such anemulsionwhich make it particularly useful as a coating or adhesive.

The use of melts and solutions of water insoluble artificial resins inthe coating and adhesive art has been supplanted to a large extent byemulsions of such resins, particularly polyvinyl acetate emulsions, dueto the improved ease, economy and safety with which aqueous emul sionsof the resin maybe employed. On the other hand, the usefulness of waterinsoluble polymer emulsions has been limited by the char acteristic lackof water-resistance of the coatings and bonds deposited therefrom atroom temperature and the tendency of such coatings and bonds tore-emulsify or disintegrate when subsequently brought into contact withwater during the course of normal use of the object or article to whichthey have been applied.

This lack of water-resistance has been considered inate in the coatingsand films deposited from such polymer emulsions inasmuch as watersolubleemulsifying and bodying agents are em. ployed necessarily to establishand stabilize the emulsion. These agents are apparently carried into thefilm or bond deposited from the emulsion upon application ofthe emulsionto a surface, and actively exhibit the emulsifying effect on the polymercomprising the body of the coating or film and cause its redispersionwhen the surface is brought into contact with water.

Various proposals have been made to obviate the water-sensitivity of thecoating or bond deposited from such emulsions, but in general theseproposals have been directed to modifying emulsions of such polymerswhich have been prepared in a specific manner, or require treating theemulsion with certain diluents immediately prior to its application dueto the recognized tendency of the suggested diluents to either break orgel the emulsion shortly after the addition of the diluent.

Prior to the instant invention, for example, a common expedient forincreasing the waterresistance of a coating or film deposited from awater-insoluble polymer emulsion included the addition of a quantity ofone or more substances such as dimethylol urea, trimethylol melamine,certain chromium salts, strong acids or highly reactive aldehydes suchas glyoxal, certain resins, toluene and peroxides. In most instances itwas required that the substances be added to the polymer emulsionimmediately prior to use as the resulting compositions were unstable andcertain of the substances resulted in a progressive increase in theviscosity of the emulsion until a gel was formed. Gelling rendered thecomposition unfit for use in adhesive applicator machines operated athigh speed. Additionally, the modification effected by some of thesesubstances did not result in a substantial improvement in thewater-resistance of the coating or film deposited from the emulsion, andoften imparted undesirable color and foaming characteristics to theemulsion.

Where thermo-plastic polymeric material has been employed, it has beensuggested that the Water-resistance of the coating or bond depositedfrom an emulsion of the material can be im proved by heating the coatingor bond sufficiently to cause coalescence of the material into ahomogeneous mass. This procedure is obviously not suitable where theemulsion is employed as a quick-setting adhesive in high-speedmechanical applicators, and in any event the drying and heatingsuggested is often impractical.

A further suggestion directed to retaining the advantages of workingwith the polymers in an aqueous medium and at the same time avoiding theinherent disadvantages of water-sensitivity of the coatings or filmsdeposited therefrom required dispersing the polymer as extremely smallparticles. The coatings or films deposited from such emulsions doexhibit a satisfactory waterresistance but due to the fine particle sizewhich imparts the water-resistance, the emulsions do not have the tacknecessary to make them useful as quick-setting adhesives.

It is an object of this invention to provide a composition comprising anaqueous emulsion of a polymer, particularly a polymer of vinyl acetate,alone or in combination with small quantities of other monomers, whichis stable throughout long periods of storage and which when employed asa coating or an adhesive will deposit a coating or bond which iswater-resistant. A further object of the invention is to provide aprocess which is generally applicable to modify emulsions of polymers,particularly polyvinyl acetate, which have been polymerized to differentextents, or in different manners, and which include various combinationsof plasticizers and other diluents commonly employed to develop favoredcharacteristics in the films or coatings deposited from such emulsions.

We have discovered that the water-resistance of coatings or bondsdeposited from an aqueous emulsion of polymers, particularly polyvinylacetate emulsions, which are formulated, or modified, to have atackiness rendering them suitable for use as quick-setting adhesives,can be established by additions of certain organic compounds withinspecific limits. These active compounds are characterized by aparticular balance between the parts of the monomeric molecule, one partof which is hydrophilic or polar in nature, and the other part of whichis hydrophobic or non-polar. The eifectiveness of the compounds inproducing water-resistance in the coatings or bonds deposited from suchemulsions is apparently due to the presence of both the polar andnon-polar groups Within the molecule in the prescribed balance. Theactive compounds exhibit solubility, to various extents, in both waterand in organic solvents such as mineral spirits, petroleum ether,toluene, castor oil, etc. This solubility in both water and organicsolvents apparently is due to the dual hydrophilic-hydrophobic nature ofthe compound. As it has been generally recognized that the presence ofwatersoluble emulsifiers carried into the bonds and coatings depositedfrom emulsions of water-insoluble polymers may later cause redispersionand disintegration of the bonds and coatings, it was particularlysurprising to find that incorporating into the emulsion additional compounds which are water-soluble to some extent themselves will'nullifythe efiect of the watersoluble emulsifiers and thereby impartwaterresistance to the coatings and films deposited from such emulsions.

For present purposes a polar or hydrophilic group or radical may beconsidered to be one which has a strong aflinlty for water and. whichwhen combined in compounds in which it is the dominant functional groupwill cause the resulting compound to be immiscible, or miscible to alimited extent, in oil-type solvents. or hydrophobic group, on the otherhand, may be considered to be one which has slight affinity for 'waterand a strong afilnity for oil-type solvents. In general, the amide groupexhibits the characteristics required of a polar group. An aryl radicalsuch as the benzyl group is a suitable non-polar group. As indicated bythe foregoing principles, it has been found that the aromatic amideshaving '7 carbon atoms are efiective in imparting water-resistance tothe coatings and bonds deposited from polyvinyl acetate emulsions inwhich they are incorporated in the quantities and manner hereafterprescribed. Benzamide, for example, has a molecule in which the benzenenucleus and a side chain which comprises one carbon atom, effectivelybalances the functional amide group of the side chain to establish therequisite polar-non-polar balance.

The number of carbon atoms in the active compounds rather than theirisomeric arrangement appears to be determinative of the degree ofnon-polarity of that portion of the compound, as where isomers existthey are all equally active.

The necessity for the prescribed polar-nonpolar balance, and theeffectiveness of the benzene nucleus in establishing such balance,appears from the fact that formamide and acetamide are entirely toohydrophilic in nature to be active in imparting water-resistance,reflecting A non-polar K the dominance of the polar amide group, whereasbenzamide is active, as previously stated.

The preferred range of quantities of one or more of the active compoundsby weight with respect to the solid content of the polyvinyl acetateemulsion has been found to be between about 23-15%, the optimum amountin a particular instance depending upon the initial waterresistancecharacteristics of the starting material emulsion, the amount ofplasticizers employed, and the age of the starting material emulsion. Inthe case of the normally solid amides, the solubility of the activecompound is the limiting factor on the amount of compound which can beemployed. In general, more than by Weight of solid content of thestarting material emulsion will tend to crystallize out. When the activecompound is normally a solid it is dissolved to obtain an effectiveconcentration and the solution thus formed is mixed with the startingmaterial emulsion.

The physical properties of a polyvinyl acetate emulsion such as theviscosity of the emulsion, and the tensile strength, flexibility andheat sealing temperature of the film or bond deposited from the emulsionare determined in a large part by the degree of polymerization of thevinyl acetate monomer. A higher degree of polymerization results inincreased bond strength, a higher heat sealing temperature and asomewhat higher initial water-resistance, which is, however,considerably less than required commercially for a water-resistantcoating or bond. A lesser quantity of the active compounds is necessaryto impart the desired water-resistance to the deposited coatings orbonds when the relatively greater water-resistant emulsions are employedas a starting material. The age of the starting material emulsion alsodetermines in part the susceptibility of the emulsion to waterproofing,the older emulsions. for example emulsions from four to six months old,show better water-resistance when treated than those freshly made.

For present purposes the polyvinyl acetate starting material emulsionshaving sufficient tack to be useful as quick-setting adhesives may beclassified in three groups according to their initial water-resistancealthough in each instance the Water-resistance is negligible from thestandpoint of minimum commercial requirements. Such emulsions generallycontain about 40-65% polyvinyl acetate by weight and a dried bondproduced by the respective emulsions between two sheets of mildlycalendered white sulphite paper will open up Within 24 hours afterimmersion in Water at about 25 C. Such emulsions include thecommercially available emulsions known as Elvacet No. -900, Elvacet81-900, Gelva 8-50 and Polyco 1171-1, Polyco 11'7-SS and Polyco 289.

The physical characteristics of the commercially available polyvinylacetate emulsions identified above may also vary to some extent as aresult of the emulsifiers and bodying agents employed in producing theemulsions, and also as a result of particular plasticizers employed. Ingeneral, however, the variations which tend to increase the relativeinitial water-resistance of the starting material emulsions lessen thequantity of the activecompounds required to efiect completewater-resistance.

The amounts of active compound required to produce maximumwater-resistance in a particular emulsion also varies with the quantityand the nature of theplasticizers, extenders, or other diluents whichmaybe-used to develop desired characteristics of fluidity or tachinessinthe emulsion, or of flexibility, hardness, etc. in the coating; or filmdeposited from the emulsion. In general, it hasbeen found that theinsoluble type'of plasticizer and resins in common use increase theeffectiveness of the active compounds, and that a lesser quantity ofactive compound is necessary to produce complete water-resistance whensuch plasticizers are also present in the emulsion. It should be noted,however, that in each instance the emulsion containing the plasticizersand various other diluents was not initially water-resistant and thatthe addition of the active compound was necessary to effect anysatisfactory water-resistance although as related above, a lesser amountis necessary when insoluble plasticizers are also present.

This enhancing effect of the insoluble plasticizers was particularlyobserved with respect to dimethyl phthalate, dibutyl phthalate,chlorinated diphenyls, methyl abiatate and tributyl phosphate, andappears to be characteristic of other common plasticizers such asdi-carbitol phthalate, dibutoxy-glycol phthalate, dimethoxy-glycolphthalate, butyl phthalyl butyl glycolate, methyl phthalyl ethylglycolate, triglycol di-Z-ethylbutyrate, triglycol cli-2-ethylhexoate,tricresyl phosphate and triphenyl phosphate.

On the other hand, the presence of a small amount of certainwater-soluble thickeners such as polyvinyl alcohol and sodiumcarboxymethyl cellulose tend to increase the amount of active compoundnecessary to eifect maximum waterresistance.

In some instances care must be exercised to avoid breaking the emulsionby sudden heating, or by extending heating above the temperaturespecified. The critical temperature will vary, of course, with thecharacter of the particular starting material emulsion employed.

Aging the composition also tends to increase the water-resistance of thecoatings or films deposited therefrom.

It will be apparent from the foregoing that innumerable possibilties forformulating the instant water-resistance composition exist, and that theinvention may be practiced to increase the water-resistance of anyparticular polyvinyl acetate emulsion without materially interferingwith the versatility of the starting material emulsion.

The addition of the active compound to the starting material emulsionmay result in a substantial increase in the viscosity of the emulsion toform a cohesive mass unless the active compound is added slowly withcontinuous agitation. In some instances rapid addition of the activecompound results in localized precipitation or" the emulsion. Thelargest part of the increased cohesiveness and viscosity of the emulsioncaused by addition of the active compound at a suitable rate disappearson agitation, or when the treated emulsion is permitted to stand for ashort period following the addition of the active compound.

In all of the following examples the composition was prepared bystirring the starting ma" terial emulsion with a high-speed mixercontinuously during the addition of the active compound thereto. Theactive compound was introduced into the emulsion at the rate of about 3%of the total weight of the active compound per minute.

Each of several tacky starting material polyvinyl emulsions was appliedas a coating on the surface of a moderately calendered. and. sized whitesulphite paper and as a bond between two such papers. The films andbonds thus formed were allowed to dry for 24 hours at room temperatureand were thereafter immersed in water at room temperature for 24 hours.Upon; removal from the water the wet strength of the paper exceeded thebond strength in all cases, and the bond ruptured when the bonded paperswere separated. The coatings in each instance had visibly disintegrated.These starting material emulsions were. therefore, considered non.-water-resistant, and in the subsequent experiments, satisfactorywater-resistance of a filmor bond formed from an emulsion treated with.an active compound. was considers fully indicated when the strength ofthe bond exceeded the wet strength of tie paper after 24 hoursimmersion.

Example 1 A sample was prepared by placing 550 parts of a polyvinylacetate emulsion having about 55% solid content in a mixing containerand stirring it with a high-speed mixer while 30' parts of a tributylphosphate plasticizer were added thereto. A solution of 24 parts ofbenzamide in parts of hot ethyl alcohol was added slowly to the mixtureof emulsion and plasticizer while it was stirred continuously.

A second sample was prepared in the same manner except that thebenzamide solution consisted of 15 parts of benzamide in 40 parts of hotethyl alcohol.

A third sample was prepared by mixing 550 parts of a polyvinyl acetateemulsion having about solid content with 30 parts of a tributylphosphate plasticizer while the emulsion was stirred continuously with ahigh-speed mixer.

All three samples were tested for water-resistance by applying thesamples as both a film and bond to a mildly sized and calendered whitesuiphite paper. The films and bonds were permitted to dry for 2% hoursand were thereafter immersed in water at room temperature for 24 hours.The iilms and bonds deposited from the samples containing the benzamidewere found to be continuous and intact after the 24 hour immersion, andthe bond strength exceeded the wet strength of the paper so that thesurface of the paper adhered to the bond when the papers were separated.The films and bonds deposited from the sample consisting of emulsion andplasticizer had visibly disintegrated during the period of immersion.The wet strength of the paper exceeded the strength of the bond and thebond fractured when the papers were separated.

Example 2 A set of three samples was prepared in the same manner asthose described in Example 1 except that the benzamide was solubilizedin about parts of hot water in place of the hot ethyl alcohol employedin Example 1. The films and bonds deposited from these three sampleswere tested for waterproofness in the manner described in Example 1. Thefilms'and bonds deposited from the samples containing the benza midewere found to be water-resistant. The films were continuous and intactafter the period of immersion and the bond strength exceeded the wetstrength of the paper so that the paper was torn when the bonded paperswere separated. The sample consisting of emulsion and plasticizer showedno water-resistance. The films had been redispersed during the period ofimmersion and the bonds fractured easily without tearing the bondedpapers when the papers were separated.

It will be apparent that the water-resistant compositions formulatedaccording to the instant invention will considerably extend theusefulness of aqueous emulsions of polyvinyl acetate into the field inwhich high water-resistance of the bond or coating deposited isnecessary and will find application in bonding or cementing forcellulosic articles such as paper cups or paper bags which in the courseof normal use are exposed to water and for bonding surfaces ofcellulosic material to other surfaces of a hydrophilic character such asmasonry. These compositions are particularly adapted for use as a sizingwhere water-resistance of the fabric or the paper to which it is appliedis required. It may also be employed in the composition of printingpaste, as a finish for paper, paper-board, or foils and in themanufacture of formed or impregnated goods, as well as distemper paintsand the like.

Having thus described the invention, what is new and desired to besecured'by Letters Patent is:

1. A composition comprising an aqueous emulsion of polyvinyl acetate,and from to 15% by weight of said acetate of an unsubstituted aromaticamide containing 7 carbon atoms.

2. A composition comprising an aqueous emulsion of polyvinyl acetate, aplasticizer for said acetate and from 5 to 15% by weight of said acetateof an unsubstituted aromatic amide containing 7 carbon atoms.

3. A composition comprising an aqueous emulsion of polyvinyl acetate,and from 5 to 15% by weight of said acetate of benzamide.

4. A process for formulating an aqueous emulsion of polyvinyl acetatecapable of depositing a water-resistant film upon evaporation of thewater phase comprising the step of adding to an emulsion of polyvinylacetate about 515% by weight of said acetate of an unsubstitutedaromatic amide having 7 carbon atoms.

5. A base having a water resistant coating deposited thereon from acomposition comprising an aqueous emulsion of polyvinyl acetate, andfrom 5 to 15% by weight of said acetate of an unsubstituted aromaticamide containing 7 carbon atoms.

6. A base having a water resistant coating deposited thereon from acomposition comprising an aqueous emulsion of polyvinyl acetate, andfrom 5 to 15% by the weight of said acetate of benzamide.

WALTER G. KUNZE. R. BERTRAM EVANS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PA'I'ENTS Number Name Date 2,098,538 Charch et a1 Nov. 9,1937 2,444,396 Collins et al June 29, 1948

1. A COMPOSITION COMPRISING AN AQUEOUS EMULSION OF POLYVINYL ACETATE,AND FROM 5 TO 15% BY WEIGHT OF SAID ACETATE OF AN UNSUBSTITUTED AROMATICAMIDE CONTAINING 7 CARBON ATOMS.